道路植被结构对大气可吸入颗粒物扩散影响的模拟与验证

为了研究道路植被结构对城市内可吸入颗粒物（简称PM10）扩散的影响，该文设计不同道路绿化布局模式，在夏季和冬季不同的风向条件下，利用三维微气候模型（ENVI-met模型）模拟大气颗粒物扩散的规律；另外，该文选择百子湾路、林大北路、交道口东大街、东直门北小街、农展馆南路6条不同绿化布局的道路作为北京市街区道路的典型案例，监测夏季和冬季不同绿化布局道路的可吸入颗粒物浓度，并与ENVI-met模型模拟结果进行对比。结果表明：在高宽比一定的情况下，乔灌草的布局方式对PM10浓度降低作用最明显，其次是乔灌组合方式，乔木对降低PM10浓度的作用较弱，灌木对降低PM10浓度的作用最弱；在植被布局相同的情况下，街道高宽比值越小，PM10浓度降低的越明显。实测和模拟结果对比发现：两者相对误差分布在10%以下的占全部的71%，相对误差分布在10%至20%占全部的22%，相对误差分布在20%以上的仅占全部的7%；模拟值和实测值拟合的决定系数R2为0.9894，RMSE为8.399 μg/m3，说明模拟结果精度较高，因此ENVI-met模型能够合理模拟道路植被结构对大气颗粒物扩散的影响，对PM10浓度降低作用角度考虑乔灌草的布局方式最优。

Simulation and verification of influence of different street vegetation structure on diffusion of atmosphere particulates

As the city is developing continuously recently, frequently occurred haze has increasingly raised residents'' concerns about the urban ecological problems. Motor vehicle exhaust gas is one of the major sources of atmospheric particulates. The road green system, an important ecological measurement, which plays a significant role in preventing the motor vehicle exhaust gas diffusion, is of great significance to improve urban air quality and residents'' life quality and the living environment. For the purpose of urban road greening plan, we used high resolution remote sensing images and street views to compile the road information tables so as to select six roads (Baiziwan Road, Linda North Road, Jiaodaokou East Avenue, Dongzhimen North Street, and Nongzhanguan South Road) in Beijing city as the sample set which represent different road green systems, green configurations and street aspect ratios. For the simulation experiment in this paper, we used three-dimensional microclimate software ENVI-met, which was based on fluid and thermodynamics (the calculation of the basic law of the fluid dynamics model), to simulate the interaction processes among ground, vegetation, building and atmosphere in a small-scale urban space. We constructed three-dimensional main model area and set main characteristic parameters of the sample places, such as building, greening and underlying surface structure, and achieved the numerical simulation of interactions among ground, vegetation, building and atmosphere by using the weather prediction subprogram to analyze governing equation. We conducted field experiment in order to compare it with the numerical simulation results. The monitoring points were set on the roadside and behind the tree respectively. Each experiment street was set with one monitoring section which has two monitoring points at the height of 1.5 meters. We selected PM10 as the monitoring item and measure meteorological factors such as wind speed, wind direction and temperature at the same time. We set the results of the non-vegetation particulate matter as background value and superposed it with the diffusion of that under different green configurations to analyze the law of particulate matter diffusion of different green configurations. The simulation results showed that, under the same condition of wind speed and wind direction, the changes of PM10 concentration on the leeward side of monitoring point were higher than that on its windward side, which proved that the motion of airflow caused the particulate matter accumulation on the leeward side and the spreading of particulate matter over the road as air flow rising, so the concentration of particles on the leeward side was the largest, and then gradually decreased as the building height increasing. Under the same condition of aspect ratio, the effect of arbor--shrub-grass configuration on reducing PM10 concentration was the most obvious, followed by the arbor--shrub configuration. The effect of arbor on reducing PM10 concentration was weak and the effect of shrub on that was the weakest. Under the same condition of green configurations, the smaller the street''s aspect ratio (the wider the street) was, the greater decrease in the concentration of PM10, which indicated that the wider street was favorable for ventilation and had the lower the concentration of pollutants and vice versa. Comparing the measured data with the numerical simulation data, the coefficient between the measured value and the simulated value was 0.9894, and the correlation between the simulated results and the field observation results was pretty high, so it could be proved that the convection-diffusion model that ENVI-met used was available for simulating the diffusion of atmosphere particulate matter and can give reasonable calculation results of the law of the diffusion of atmosphere particles.